An Automatically Switched Optical Network (ASON) is a type of dynamically and automatically switched transport network. It's a new generation optical network, where: a service request is originated dynamically by users; a path is calculated and selected automatically by a network element; setup, restoration and clearance of a connection are controlled by signaling; and switching and transporting are integrated. An ASON includes two layers: a control plane and a transport plane. Main functions of a control plane include: collecting and distributing network topology of an ASON; forming a “network map” describing network topology; calculating a viable path through routing algorithms and by use of the “network map”, and establishing an intelligent circuit using a signaling protocol for each node on the path. Functions of a transport plane include setting up or deleting cross-connections on each network element, and establishing or withdrawing services on the transport plane, according to instructions from a control plane.
Wavelength Division Multiplexing (WDM) is a technology to transport services with various wavelengths. Rapid increases of image and data services cause tremendous demands for network bandwidth, and the conventional WDM technology is intended to meet such bandwidth demands. A WDM device can be divided into a long-distance WDM device and a metropolitan WDM device. A long-distance WDM device is commonly used as a national trunk or a regional trunk, for long-distance and high-capacity transmissions. A metropolitan WDM device is mainly used for data service transmissions in rapidly developing metropolitan networks. Traditional WDM networks are point-to-point static networks. However, the emergence of Reconfigurable Optical Add/Drop Multiplexer (ROADM)/Wavelength Selective Switching (WSS) technology makes dynamic WDM networks possible; so that vendors are able to provide new services, and add or modify network services dynamically, without the need to redesign networks. In addition, combining WDM devices and ASON technology can reduce operational expenditures.
However, because of certain optical limitations existing in WDM devices and due to low integrity, cross-connection constraints may exist in WDM devices (i.e. there may be blocking in wavelength switching of WDM devices), which may not be like Synchronous Digital Hierarchy (SDH), where one channel may be easily cross-connected to another. Cross-connection constraints cause problems in path calculations in an ASON. Moreover, in a WDM network, sometimes it may not be possible to establish a wavelength service between two nodes that are reachable in topology and have resources available.
Previous solutions have provided abstract models to determine reachability information between access points of a network; thus, solving certain blocking and constraint problems in pure photonic Generalized Multiprotocol Label Switching (GMPLS) network sub-domains. For example, in an abstract model, a pure photonic GMPLS network may be abstracted into a logical or abstract cloud, and reachable information among access points of a Generalized Label Edge Router (GLER) is abstracted. With this abstract model, less information is distributed among GLER nodes. Due to insufficient information distributed, however, a label set would have to be used to restrict selection of wavelengths at setup time. Thus, even if such a restriction is applied, the rate for establishing a successful service path is low.
In another abstract model, a Generalized Label Switching Router (GLSR) node in a pure photonic GMPLS network may be abstracted into a logical/abstract GLSR node, and reachable information of links associated with a logical GLSR node is abstracted and distributed to other nodes. Information involved in this abstract model is large, but relatively complete. Therefore a higher rate of successful path calculations may be obtained when compared with the first model. In a WDM network, however, although a link may be reachable, it does not necessarily mean that wavelength is reachable. Thus an established service path may not necessarily be viable. For this reason, a crankback technology may need to be used, to repeatedly attempt to establish a service path.
Therefore, such conventional methods may not produce correct service path calculations. This can greatly decrease service setup efficiency, especially in cases where a service is restored after interruption. Repeated attempts are intolerable, because a new path should be computed and a service should be re-established as soon as possible. Another drawback is caused by high frequency of information distribution, since a link's reachability changes once a service is established, and such information must be updated in real-time, and distributed through out a whole network. This in turn, places a large demand overhead on a network.
Another conventional method typically configures services manually and statically using a network management system. For less powerful network management systems, manually designed configurations may be created and then distributed station by station. Powerful network management systems normally collect cross-connection capabilities and cross-connection constraints of each WDM device, and then calculate an appropriate path after considering the collected information.
However, manually designing and distributing configuration services is cumbersome, time-consuming and difficult to maintain. Moreover, automatically calculating service paths is similar to a centralized ASON, which is unsafe, heavy in network management system workload, and is difficult to reroute services dynamically.
Therefore, there is a need to overcome cross-connection constraint issues in a WDM device for an intelligent WDM network. There is also a need to provide correct service path calculations, and to decrease information distribution workload.